setenv(3)                  Library Functions Manual                  setenv(3)

NAME
       setenv - change or add an environment variable

LIBRARY
       Standard C library (libc, -lc)

SYNOPSIS
       #include <stdlib.h>

       int setenv(const char *name, const char *value, int overwrite);
       int unsetenv(const char *name);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       setenv(), unsetenv():
           _POSIX_C_SOURCE >= 200112L
               || /* glibc <= 2.19: */ _BSD_SOURCE

DESCRIPTION
       The setenv() function adds the variable name to the environment with
       the value value, if name does not already exist.  If name does exist in
       the environment, then its value is changed to value if overwrite is
       nonzero; if overwrite is zero, then the value of name is not changed
       (and setenv() returns a success status).  This function makes copies of
       the strings pointed to by name and value (by contrast with putenv(3)).

       The unsetenv() function deletes the variable name from the environment.
       If name does not exist in the environment, then the function succeeds,
       and the environment is unchanged.

RETURN VALUE
       setenv() and unsetenv() functions return zero on success, or -1 on
       error, with errno set to indicate the error.

ERRORS
       EINVAL name is NULL, points to a string of length 0, or contains an '='
              character.

       ENOMEM Insufficient memory to add a new variable to the environment.

ATTRIBUTES
       For an explanation of the terms used in this section, see
       attributes(7).

       +--------------------------------+---------------+---------------------+
       |Interface                       | Attribute     | Value               |
       +--------------------------------+---------------+---------------------+
       |setenv (), unsetenv ()          | Thread safety | MT-Unsafe const:env |
       +--------------------------------+---------------+---------------------+
STANDARDS
       POSIX.1-2008.

HISTORY
       POSIX.1-2001, 4.3BSD.

       Prior to glibc 2.2.2, unsetenv() was prototyped as returning void; more
       recent glibc versions follow the POSIX.1-compliant prototype shown in
       the SYNOPSIS.

CAVEATS
       POSIX.1 does not require setenv() or unsetenv() to be reentrant.

BUGS
       POSIX.1 specifies that if name contains an '=' character, then setenv()
       should fail with the error EINVAL; however, versions of glibc before
       glibc 2.3.4 allowed an '=' sign in name.

SEE ALSO
       clearenv(3), getenv(3), putenv(3), environ(7)

Linux man-pages 6.7               2023-10-31                         setenv(3)